Method and apparatus for generation of gray scale in gaseous discharge panel using multiple memory planes

ABSTRACT

A method and system for producing a gray scale on a gaseous discharge panel. A number of gray level ranges are defined and a number of memory planes equal to the number of gray level ranges are provided, each memory plane having the same number of storage areas as the number of storage and discharge areas in the display panel. An image field is scanned with a vidicon tube and the elements of the signal corresponding to the picture elements are digitized according to the gray level range in which they fall and are fed in sequence to the memory plane corresponding to that gray level. The contents of each memory is then read out to excite the display panel beginning with the memory corresponding to the brightest gray level range and ending with the memory corresponding to the dimmest gray level range. Due to thestorage characteristics of the panel, the bits read from the memory corresponding to the brightest grey level range excite corresponding discharge areas of the display panel for a longer period of time than the bits from the memory planes corresponding to the dimmer gray level ranges and the resulting display picture has gradations of gray corresponding to the original scanned image.

United States Patent Schmersal et a1.

[451 Jan. 28, 1975 METHOD AND APPARATUS FOR GENERATION OF GRAY SCALE INGASEOUS DISCHARGE PANEL USING MULTIPLE MEMORY PLANES [75] Inventors:Larry J. Schmersal; Theodore C.

Baker; Ellsworth M. Murley, all of Toledo,-,Ohio

[73] Assignee: Owens-Illinois, lnc., Toledo, Ohio [22] Filed: Feb. 28,I973 [21] Appl. No.: 336,599

[52] US. Cl. 178/6, 178/73 D, 315/169 TV,

[51] Int. Cl. H04n 5/70 [58] Field of Search 4, 178/6, 7.3 D; 315/169 R,

315/169 TV; 313/108 A, 108 B; 340/324 M [56] References Cited UNITEDSTATES PATENTS 3,590,156 6/1971 Easton 178/75 D 3,627,924 12/1971Flemingm. 178/73 D 3,739,084 6/1973 Heinrich 178/6 PrimaryExaminer-Howard W. Britton Assistant Examiner-Michael A. MasinickAttorney, Agent, or FirmDonald Keith Wedding; E.

J. Holler [57] ABSTRACT A method and system for producing a gray scaleon a gaseous discharge panel. A number of gray level ranges are definedand a number of memory planes equal to the number of gray level rangesare provided, each memory plane having the same number of storage areasas the number of storage and discharge areas in the display panel. Animage field is scanned with a vidicon tube and the elements of thesignal corresponding to the picture elements are digitized according tothe gray level range in which they fall and are fed in sequence to thememory plane corresponding to that gray level. The contents of eachmemory is then read out to excite the display panel beginning with thememory corresponding to the brightest gray level range and ending withthe memory corresponding to the dimmest gray level range. Due tothestorage characteristics of the panel, the bits read from the memorycorresponding to the brightest grey level range excite correspondingdischarge areas of the display panel for a longer period of time thanthe bits from the memory planes corresponding to the dimmer gray levelranges and the resulting display picture has gradations of graycorresponding to the original scanned image.

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26 -"'f LINE LINE 1 r 12.0 uv/Tut PULSE LINE METHOD AND APPARATUS FORGENERATION OF GRAY SCALE IN GASEOUS DISCHARGE PANEL USING MULTIPLEMEMORY PLANES This invention relates to a method and system forproducing a gray scale in a gaseous discharge storage and display panel.Since a gaseous discharge panel such as a plasma panel is an on-offdevice, light intensity emitted therefrom cannot inherently be varied.This represents a serious disadvantage for a display device as it isfrequently desirable to display an image having variable shades ofbrightness.

It has been discovered that the apparent light intensity of thedischarge areas of a gaseous discharge panel can be varied by pulsingthe discharge areas on and off very rapidly so that the persistence ofvision of the eye averages the light. As the ratio of on time to offtime is increased, the apparent intensity of the light emitted by thedischarge area increases. Thus, the gray scale can be produced byvarying the on/off time of the discharge areas and if the on/off time ofeach discharge area is controlled, a half-tone picture can be displayed.

It is thus an object of the invention to provide a method and apparatusfor producing a gray scale in a gaseous discharge panel.

It is a further object of the invention to provide a method andapparatus for displaying a half-tone picture with a gaseous dischargepanel.

The above objects are accomplished by providing a number of memoryplanes equal in number to the number of gray level ranges to bereproduced. Each memory plane has the same number of storage areas asthe number of storage and discharge areas that the display panel has. Animage is scanned and the picture elements are separated into a finitenumber of shades of gray, equal in number to the number of memory planesprovided. Each picture element is stored in its proper sequence in amemory plane associated with the shade of gray that the picture elementcorresponds to, and the contents of the memory planes are then sequencedinto the panel to reproduce the original picture.

FIG 1 is a diagram of a system according to an embodiment of theinvention.

FIG. 2 is a detailed drawing of the A to D level converter 5 of FIG. 1.

The object of the system shown in FIG. I is to produce a gray scale ingaseous discharge storage and display panel 23. Panel 23 can, forinstance, be the storage and display panel disclosed in US. Pat. No.3,499,167 assigned to the same assignee as the present application. Thepanel disclosed in that patent is a crossedconducting element panelwhich emits light locally at areas corresponding to the cross-over areasof two conducting elements when the two conducting elements are excitedwith the required voltage. A sustaining voltage may be applied to all ofthe conducting elements to insure that a discharge area remains excitedafter initial excitation and is therefore also a memory area, until thedischarge is extinguished by removing the sustaining voltage.

In FIG. 1, memory planes I4, l5, l6 and 17, which can be ferrite corearrays each have the same number of storage areas as the discharge panel23. One memory plane is required for each shade of gray desired. Fourare shown, but more or less can be used if desired. While for ease ofillustration, only eight storage areas per line are shown in the memoryplanes and discharge panel of FIG. 1, in an actual device, 200 or moreareas per line could be used. The essential idea of the invention is tobreak down the picture elements being scanned into a finite number ofshades of gray. store each shade of gray in proper sequence in its ownmemory plane, and then sequence the contents of each memory plane intothe discharge panel to reproduce the original picture.

The system of FIG. 1 shows a vidicon tube as the primary analog picturepick-up device. A vidicon has been chosen in this embodiment because itallows sufficient speed to reproduce TV pictures on a discharge panel,but it should be understood that other pick-up devices can be used. Thevidicon sweeps a raster by making the horizontal sweep frequency of thevoltage generated by horizontal sweep generator 2 many times thevertical sweep frequency of the voltage generated by vertical sweepvoltage generator 3. In order to make the number of raster linescorrespond to the number of rows in memory planes l4, l5, l6 and 17 theratio of the horizontal sweep frequency to the vertical sweep frequencyis made equal to the number of rows in each memory plane. Row and columncoupler 6 has a plurality of row conducting elements 370 to 37h equal innumber to the number of rows of conducting elements 38a to 3812 ofmemory plane I4 and a number of column conducting elements 39a to 3911equal in number to the number of columns of conducting elements 400 to40h of memory plane 14. Row and column couplers 8, 10 and 12 likewisehave row conducting elements and column conducting elements whichcorrespond respectively to the row and column conducting elements ofmemory plane I5, 16 and 17. Elements 37a to 37h are connected toelements 38a to 38h and elements 39a to 3911 are connected to elements40a to 40h and elements of the other couplers are connected tocorresponding elements of the other memory planes so that bysimultaneously activating a row conducting element and a column elementof a coupler an information bit is stored at a corresponding location inthe panel 23.

In the embodiment shown in FIG. 1 four gray level ranges of the image tobe scanned are decided upon. A to D level converter 5 explained ingreater detail in FIG. 2 is arranged to generate; an output signal online 40 when the output of the vidicon has a signal corresponding to thebrightest gray level range, an output signal on line 39 when the outputof the vidicon is a signal corresponding to the next brightest range, asignal on line 38 when the vidicon output corresponds to thenext-to-the-dimmest range and an output on line 37 when the vidiconoutput corresponds to the dimmest gray level range. Memory plane 17 willthus store bits corresponding to picture elements in the brightestrange, memory plane 16 will store bits corresponding to picture elementsin the next-to-brightest range, memory plane 15 will store bitscorresponding to elements in the nextto-the-dimmest range and memoryplane 14 will store bits corresponding to elements in the dimmest range.

While for ease of illustration the outputs 60 and 61 of row and linesequencer 9 are shown as only being connected to row and column couplers6, they are actually coupled to each of the row and column couplers inthe same fashion and while only line 37 is being shown connected tocoupler 6 through AND'gate 41, together with row line 60, actually eachof the lines 38, 39 and 40 are connected to row and column couplers 8, land 12 by being AND gated with the output of row line 60. Hence, theinputs to each of the couplers is identical, except that a differentoutput of level converter 5 is AND gated with row line 60 in each case.Write oscillator 7, which can for instance be an astable multi-vibratorprovides pulses to row and line sequencer 9 which is synchronized by thehorizontal and vertical sweep generators 2 and 3 to provide outputpulses on lines 60 and 61 which pulses, if AND gate 41 and correspondingAND gates associated with the other couplers were not present. would beoperative to provide pulse signals to all of the couplers in row-byrowsequence in synchronism with the scanning of the raster, and memoryplanes 14, 15, 16 and 17 would be filled with l bits in row-by-roworder, Due, however, to the presence of AND gate 41, and thecorresponding AND gates associated with the other couplers 1 bits aresupplied only to the memory planes associated with the gray level rangewhich corresponds to the picture element from which the bit is derived.Hence, as the vidicon scans a raster l bits are entered to the memoryplanes in synchronism and in positional correspon dence with thescanning elements of the picture with bits derived from elements indifferent gray level ranges being entered to different memory planes.After an entire frame is scanned, memory plane 17 will have bits storedat storage areas corresponding to image locations where the brightestpicture elements occur, memory plane 14 will have bits stored at storageareas corresponding to image locations where the dimmest pictureelements occur and memory planes 15 and 16 will have bits correspondingto elements of intermediate brightness stored therein.

In an actual embodiment row and line sequencer 9 would include a rowcounter and a line counter, each having 8 output lines and representedfor ease of illustration in FIG. 1 as single output lines 60 and 61.Each of the 8-row output lines would be AND gated in a separate AND gatewith lines 37 and the outputs of the AND gates would be connected toconducting ele ments 39a to 39h while the line counter output lineswould be connected to conducting elements 37a to 37h. The row counterwould count the output pulses of write oscillator 7 while the linecounter would count the horizontal sweep signals so that an output pulsewould be supplied to element 37a by the line counter while the rowcounter stepped through eight pulses supplied to the AND gatesassociated with the element 390 to 39h. The line counter responsive tothe next horizontal sweep signal would then supply a pulse to element37b while the row counter would again supply eight pulses to the ANDgates associated with lines 39a to 39h. The same procedure would takeplace in each of the other row and column couplers 8, l0 and 12.

The information is extracted from the memories by read oscillator 18operating in conjunction with the read-out pulse generator 19. Readoscillator 18 may be any standard pulse generator which generates apulse train of constant frequency such as an astable multivibrator. Readoscillator 18 is arranged to operate at a much higher frequency thanwrite oscillator 7, the frequency of oscillator 18 being limited only bythe time required to subtract a bit from the memory planes. To avoidcross-talk when reading and writing simultaneously read and writeoscillators l8 and 17 are operated asynchronously.

In an actual embodiment. the read-out pulse generator 19 would becomprised of four read-out row and column couplers such as 6, l8, l0 and12 operating in combination with a row and line sequencer pro- 5 grammedto activate the conducting elements of the couplers in line-by-linefashion. Unlike the writing process, however, the reading would not besynchronized with the sweep voltage of the vidicon. but rather. asindicated above, would be as fast as permitted by the time it would taketo extract a bit from the memory planes. For ease of illustration.read-out generator 19 is illustrated as a block in FIG. 1 with leads 45.46. 47 and 48 respectively being arranged to read-out memory plane 17,l6, l5 and 14. To eliminate cross-talk while reading and writingsimultaneously while the information is written in horizontal rowsread-out pulse generator 19 is arranged to read the information out invertical columns. Generator 19 is further arranged to have an initialoutput pulse line 70 and a final output pulse line 30 on which pulsesappear shortly after the initial read-out pulse is generated and shortlyafter the final read-out pulse is generated respectively. Lines 30 and70 may for instance be connected through delay networks to theappropriate stages of the counter network of generator 19. Additionally,generator 19 is also arranged to have a column line output 29 whichgenerates a pulse shortly after the last read-out pulse in each columnappears and which can also be connected through a delay network to anappropriate stage of the counter network.

The bits of brightest gray level range memory plane 17 are read outfirst column-by-column by read-out signals on line 45. After the firstread-out pulse is generated, a signal appears on line 70 which signal isoperative to trigger row and column sustaining voltage generator 35 tothe on-state. The voltage supplied to the row and column elements bygenerator 35 is not high enough to trigger the panel to emit light, butis high enough to sustain an emission after triggering occurs. The bitsare fed out of the memory plane on sense line 24 to shift register 20which receives a series shift pulse on line 28 with each pulse generatedby read oscillator 18. After an entire column of bits is entered toshift reg ister 20 a signal indicating the end of the column isgenerated on line 29 which signal is fed on line 50 to shift register 20and which is operative to parallel shift the column of hits out of theshift register to display panel 23. The signal on column line 29 is alsofed to line 31 where it activates counter 21, the outputs of whichselectively actuate the output conductors of panel pulse generator 22.While in an actual embodiment, counter 21 would have eight output linesconnected to the eight conductors at panel 22, for ease of illustrationa single output line 51 is illustrated. Thus, at the same time that therows of bits are shifted out of register 20, the output conductor ofpanel pulse generator 22 corresponding to column of the memory planeread out is activated and the net column and row voltage is sufficientin combination with the sustaining voltage to cause an areacorresponding to the cross-over area of the activated row and columnactivated to emit light. The bits can be re-written after being readout.

The panel will thus first be excited at appropriate locations by all ofthe bits read from brightest gray level range memory plane 17. After asuitable delay produeed by delay means 42, read-out pulse generator 19causes the columns of next-to-brightest memory plane 16 to be read outon sense line by read-out signals on line 46. In the same fashion asexplained in conjunction with memory plane 17, the bits of memory plane16 are fed through shift register 20 to excite the appropriate locationsof display 23.

After a delay introduced by delay means 43, panel 23 is excited by thebits of next-to-dimmest memory panel 15 and after a delay introduced bydelay means 44 panel 23 is excited by the bits of dimmest memory plane14. After the final bit of memory plane 14 is read out, a signal isgenerated on final pulse line which after being delayed for a suitabletime in delay means 53, feeds a turn-off signal to sustaining voltagegenerator 35. The removal of the sustaining voltage extinguishes thepanel and immediately after turn-off, readout pulse generator 19 beginsto read-out memory plane 17 once again and the entire process isrepeated. The frame rate of construction is made fast enough so that noflicker appears.

FIG. 2 illustrates the A to D level converter 5 of FIG. 1 in greaterdetail. In FIG. 2 the outputs of vidicon 4 are fed to level detectors80, 81, 82 and 83 which may, for instance, be Schmitt triggers. Theoutput of the level detectors are arranged to be in the one state untilthe input signal to the detector exceeds the predetermined amplitudelevel at which time the output changes to the zero state. Zero stateoutput line 84 from level detector 80 and one state output line 85 fromlevel detector 81 are fed to AND gate 91. Likewise, zero state outputline 86 of level detector 81 and one state output line 87 of leveldetector 82 are fed to AND gate 92 and zero output line 88 of leveldetector 82 and one state output line 99 of level detector 83 are fed toAND gate 93. Output lines 37, 38, and 39 from AND gate 91, 92 and 93respectively, are fed to row and column couplers 6, 8 and 10 and zerostate output line from level detector 83 is fed to row and columncoupler 12 as shown in FIG. 1.

When the output signal of vidicon 4 is greater than the triggering levelof level detector 80 but less than the triggering level of leveldetector 81 then level detector 80 will be in the zero state and leveldetector 81 will be in the one state and signals will appear on lines 84and 85 simultaneously thus causing AND gate 91 to generate an outputsignal on line 37. Likewise, when the output signal of the vidicon isgreater than the triggering level of level detector 81 but less than thetriggering level of level detector 82, then level detector 81 is in thezero state and level detector 82 is in the one state and signals appearon lines 86 and 87 simultaneously causing an output signal to begenerated by output line 38 of AND gate 92. In a similar fashion, whenthe output signal from the vidicon is between the triggering level oflevel detector 82 and the triggering level of level detector 83, ANDgate 93 will generate an output on output line 39. When the vidiconoutput signal is greater than the triggering level of level detector 83,an output appears on zero state output line 40. Lines 37, 38, 39 and 40are fed to the row and column couplers 6, 8, 10 and 12 as shown in FIG.1.

Thus there has been described a preferred embodiment ofa method andsystem for producing a gray scale in a discharge and storage panel.

While we have disclosed and described the preferred embodiments of ourinvention, we wish it understood that we do not intend to be restrictedsolely thereto, but that we do intend to include all embodiments thereofwhich would be apparent to one skilled in the art and which come withinthe spirit and scope of our inventron.

We claim:

1. A system for producing a gray scale in cross conductor gas dischargeand display panel having a plurality of crossing areas which correspondto a plurality of display and storage areas comprising,

means for scanning an image field and generating an image signalcorresponding thereto,

a plurality of separate storage means for storing signals correspondingto each of a plurality of gray level ranges from a brightest range to adimmest range,

each of said storage means having at least as many discrete storagepositions as said panel has crossing areas, said positions in each ofsaid storage means being in geometrical correspondence with thepositions of said crossing areas in said panel,

means for routing signals derived from said image signal to differentones of said storage means dependent on the amplitude of said imagesignal in synchronism with the scanning of said field so that saidsignals derived from image signals within each amplitude range whichcorresponds to a different gray level are stored in the storage meanscorresponding to that gray level at positions which correspond to theirposition in said scanning field,

means for sequentially exciting said panel with signals corresponding tothe signals stored in each of said storage means beginning with signalsfrom said storage means corresponding to said brightest range and endingwith signals from said storage means corresponding to said dimmest rangeso that the crossing areas corresponding to the storage positions whichstored signals therein are excited, said means for sequentially excitingincluding means for exciting the panel with signals corresponding to allstored signals in a storage means before the panel is excited withsignals from the storage means corresponding to the next dimmest graylevel and also including delay means of arbitrary delay time controllingthe delay between excitation of the panel with signals from one storagemeans and with signals from the next storage means,

and means for extinguishing the entire panel at the same time, saidpanel remaining in the excited state until extinguished, whereby saidsignals corresponding to each gray level range cause said panel to beexcited for a longer period of time than the signals from each dimmergray level range, thereby producing said gray scale.

2. The system of claim 1 wherein said means for exciting includes ashift register means and means for reading the signals stored in eachrow or column of storage positions of each of said storage meanssequentially into said shift register.

3. The system of claim 2 further including means for parallel shiftingeach row or column of signals which is read into said shift register outof said shift register for exciting a row or column of said displaypanel.

4. A method for producing a gray scale in a cross conductor gasdischarge and display panel having a plurality of crossing areas whichcorrespond to a plurality of display and storage areas comprising,

scanning an image field and generating an immage signal correspondingthereto,

providing a plurality of separate storage means for storing signalscorresponding to each of a plurality of gray level ranges from abrightest range to a dimmest range, each of said storage means having atleast as many discrete storage positions as said panel has crossingareas, said positions in each of said storage means being in geometricalcorrespondence with the positions of said crossing areas in said panel,

routing signals derived from said image signal to different ones of saidstorage means dependent on the amplitude of said image signal insynchronism with the scanning of said field so that said signals derivedfrom image signals within each amplitude range which corresponds to adifferent gray level are stored in the storage means corresponding tothat gray level at positions which correspond to their position in saidscanning field, sequentially exciting said panel with signalscorresponding to the signals stored in each of said storage meansbeginning with signals from said storage means corresponding to saidbrightest range and ending with signals from said storage meanscorresponding to said dimmest range so that the crossing areascorresponding to the storage positions which stored signals therein areexcited. the delay time between exciting said panel with signals fromone storage means and signals from the next storage means beingpredetermined but arbitrary,

and extinguishing the entire panel at the same time.

said panel remaining in the excited state until extinguished wherebysaid signals corresponding to each gray level range cause said panel tobe excited for a longer period of time than the signals from each dimmergray level range, thereby producing said

1. A system for producing a gray scale in cross conductor gas dischargeand display panel having a plurality of crossing areas which correspondto a plurality of display and storage areas comprising, means forscanning an image field and generating an image signal correspondingthereto, a plurality of separate storage means for storing signalscorresponding to each of a pluraLity of gray level ranges from abrightest range to a dimmest range, each of said storage means having atleast as many discrete storage positions as said panel has crossingareas, said positions in each of said storage means being in geometricalcorrespondence with the positions of said crossing areas in said panel,means for routing signals derived from said image signal to differentones of said storage means dependent on the amplitude of said imagesignal in synchronism with the scanning of said field so that saidsignals derived from image signals within each amplitude range whichcorresponds to a different gray level are stored in the storage meanscorresponding to that gray level at positions which correspond to theirposition in said scanning field, means for sequentially exciting saidpanel with signals corresponding to the signals stored in each of saidstorage means beginning with signals from said storage meanscorresponding to said brightest range and ending with signals from saidstorage means corresponding to said dimmest range so that the crossingareas corresponding to the storage positions which stored signalstherein are excited, said means for sequentially exciting includingmeans for exciting the panel with signals corresponding to all storedsignals in a storage means before the panel is excited with signals fromthe storage means corresponding to the next dimmest gray level and alsoincluding delay means of arbitrary delay time controlling the delaybetween excitation of the panel with signals from one storage means andwith signals from the next storage means, and means for extinguishingthe entire panel at the same time, said panel remaining in the excitedstate until extinguished, whereby said signals corresponding to eachgray level range cause said panel to be excited for a longer period oftime than the signals from each dimmer gray level range, therebyproducing said gray scale.
 2. The system of claim 1 wherein said meansfor exciting includes a shift register means and means for reading thesignals stored in each row or column of storage positions of each ofsaid storage means sequentially into said shift register.
 3. The systemof claim 2 further including means for parallel shifting each row orcolumn of signals which is read into said shift register out of saidshift register for exciting a row or column of said display panel.
 4. Amethod for producing a gray scale in a cross conductor gas discharge anddisplay panel having a plurality of crossing areas which correspond to aplurality of display and storage areas comprising, scanning an imagefield and generating an immage signal corresponding thereto, providing aplurality of separate storage means for storing signals corresponding toeach of a plurality of gray level ranges from a brightest range to adimmest range, each of said storage means having at least as manydiscrete storage positions as said panel has crossing areas, saidpositions in each of said storage means being in geometricalcorrespondence with the positions of said crossing areas in said panel,routing signals derived from said image signal to different ones of saidstorage means dependent on the amplitude of said image signal insynchronism with the scanning of said field so that said signals derivedfrom image signals within each amplitude range which corresponds to adifferent gray level are stored in the storage means corresponding tothat gray level at positions which correspond to their position in saidscanning field, sequentially exciting said panel with signalscorresponding to the signals stored in each of said storage meansbeginning with signals from said storage means corresponding to saidbrightest range and ending with signals from said storage meanscorresponding to said dimmest range so that the crossing areascorresponding to the storage positions which stored signals therein areexcited, the delay time between exciting said panel with signals fromone storage mEans and signals from the next storage means beingpredetermined but arbitrary, and extinguishing the entire panel at thesame time, said panel remaining in the excited state until extinguishedwhereby said signals corresponding to each gray level range cause saidpanel to be excited for a longer period of time than the signals fromeach dimmer gray level range, thereby producing said gray scale.